A display device such as a mobile terminal, a tablet, a touch panel and PDA (Personal Digital Assistant) generally employs a tempered glass which is chemically reinforced. The tempered glass configures a glass base material and a surface reinforced layer (chemically reinforced layer) on its top surface. This configuration enables the tempered glass having the thinner thickness while realizing the higher strength against bending stress and impact.
Processing a tempered glass having a surface reinforced layer of a certain thickness or more and a certain surface compression stress or more (for example, the thickness of the surface reinforced layer is 40 μm or more, and the surface compression stress is 600 MPa or more) is not easy. Accordingly, Patent Publication 1 describes a method of processing the tempered glass having the surface reinforced layer of 30 μm or less and the surface compression stress of 600 MPa or less which is processed by employing a known cutting method (such as laser beam machining). Further, Patent Publication 2 proposes a method of processing a tempered glass (the thickness of the surface reinforced layer is 40 μm or more, and the surface compression stress is 600 MPa or more) by removing, at an expected cutting position, a part of the surface reinforced layer that is weakening the processing strength. Then, in this method, an expected cutting trench is formed and cut by using a laser.